If you get 404 errors on local tag URLs when using the UltimateTagWarrior plugin on WordPress 2.X, it’s because the internal rewrites generated by WordPress are being overly greedy and getting invoked before UTW’s rewrite rules have a chance. This usually occurs only when using a custom permalink structure (like /%postname%/). To fix it, either switch your Permalink structure to “Date and name based” or hack the UTW plugin to place the UTW rewrites at the top of the internal rewrites array.